A. Field of the Invention
The present invention relates to a Contact-type Image Sensor (CIS) flatbed scanner, especially to a CIS scanner having a conveying device of a shape of a twisted closed loop for driving the Contact-type Image Sensor module (CIS module) in balance while still capable of keeping an original sheet within the scene depth of the CIS module.
B. Description of the Prior Art
A CIS scanner is a flatbed scanner that uses a CIS contact sensor for converting image signals into electric signals. A CIS contact sensor is a compact module which mainly includes light sources, mirrors, and a photoelectric converting device. The application of CIS module in a flatbed scanner has several advantages. For instance, it can simplify the inner structure of a scanner, reduce the size of a scanner, and make the scanner more easy to assemble and maintain.
Nevertheless, this approach did not prevail because of several difficulties in the conveying structure of the CIS scanner and the restrictions of its scene depth. The CIS module is in bar-like shape. A conventional conveying device drags the CIS module from one side because it only uses one driven motor. If the CIS module is driven by a conventional driving device from one of its bracket arm, the CIS module will easily become unbalanced while being dragged along the sheet table. If we want to use the conventional conveying device to drag the CIS module from both of its bracket arms, then it may needs two driving motors. That will inevitably increase the manufacture cost. In addition to these problems, the main reason for why the CIS scanner is not popular is because the scene depth of the CIS module is only about 0.3 mm. It is difficult for a conventional CIS scanner to assure a document sheet in focus while the CIS module being dragged along the sheet table.